Manganese-doped MnSe/CdSe core/shell nanocrystals: Preparation, characterization, and study of growth mechanism
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cleation doping strategy is an effective doping method; herein the synthesis of MnSe/CdSe nanocrystals using this strategy with different anion precursors was demonstrated. The resulted nanocrystals were characterized by various test technology to confirm the composition and structure. Wurtzite CdSe shell was achieved without using alkylphosphine, this is meaningful for the development of green chemistry. It is argued that the shell growth is more like a second nucleation process, rather than the epitaxial growth; this conclusion is believed to shed some light on the nucleation doping process. I. INTRODUCTION
Intentional incorporation of impurities into colloidal nanocrystals is essential to tune the electronic, optical, and magnetic properties of their corresponding bulk semiconductors.1–3 The unique properties of these nanocrystals, arising from the small volume and quantum confinement effects, promise several potential applications in biolabeling,4 lasers,5 light-emitting diodes,6 etc. Especially, doping nanocrystals with transition metal ions such as Mn21 produces so called diluted magnetic semiconductor that could be used in spintronic devices because of the effect termed as the giant Zeeman splitting, which results from the exchange interaction between the transition metal ions and the electronic states of the host nanocrystals.2,7 As a result, the control of doping nanocrystals with transition metal ions is of fundamental interest in scientific research and in the application of spintronics. Nucleation doping strategy is an effective doping method for synthesizing the core/shell structure, which has several advantages. First, the core nanocrystals are passivated with a wider gap material to improve the fluorescence efficiency and stability against photo-oxidation, this is because, in such a system, the surface-related trap states acting as nonradiative process were suppressed.8 In addition, either the lattice mismatch between the core and shell or the large splitting of Mn21 excited state resulted from the thin thickness of the shell could induce the color tunability, which is the red shift or blue shift, respectively,9,10 thus widening the window of Mn21-doped semiconductor phosphors. It is known that such onion-like structure can be constituted by
different compositions such as MnS/CdS,9 MnS/ZnS,11 and MnSe/ZnSe.12 However, in these heterojunctions, the core and shell are in the same structure phase. To our best knowledge, there is no report on the synthesis of nanocrystals with core and shell in different structure. Systematic researches have been carried out to study the effects of ligands on the formation of CdSe nanocrystals in different structures.13 In all the cases to synthesize CdSe nanocrystals, it is well known that the condition of selenium precursors prepared with alkylphosphine would lead to wurtzite structure.14 However, such alkylphosphine is pyrophoric, expensive, and toxic, the experimental condition needs carefully controlled. Then greener protocols were developed by dispersing selenium in oct
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